Glaciers and the work of IceQuestions to meditate upon while gazing at a Lava LampPowerPoint PresentationSlide 4Slide 5Accumulation and AblationTo make glaciersSlide 8Slide 9Glaciers begin with snowSlide 11Slide 12Glacial movementSlide 14Glacial movement (ice flow)Slide 16Internal Glacial movement (ice flow)Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Glacial ErosionSlide 25Slide 26Slide 27Slide 28Slide 29Glacial DepositionSlide 312 Broad categories of GlaciersSlide 33Slide 34Valley GlaciersSlide 36Slide 37Slide 38Erosional featuresSlide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Continental GlaciersSlide 48Slide 49Slide 50Continental Glaciers and Ice sheetsSlide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Slide 63Slide 64Slide 65Slide 66Slide 67Slide 68Slide 69Slide 70Slide 71Slide 72Slide 73Glaciers and Glaciers and the work of Icethe work of IceLecture 34 & 35Lecture 34 & 35Questions to meditate upon while gazing at a Lava Lamp•How do glaciers form and move?•Why are glaciers so important to the hydrologic cycle? Why are these so important to the formation of sediment?•How is a glacier like a Rock?What is a glacier?•An open system of flowing ice–Water input as snow–Transformed into ice–Ice flows under pressure–Water leaves by evaporation and melting, calvingGlacial Ice•Glaciers maintain a balance of ice–Zone of accumulation - net gain in ice–Zone of ablation - net loss of ice–Snow line - boundary between zones•Changes in climate shift the position of the snow lineAccumulation and Ablation•Accumulation – the addition of snow/ice to glacial system•Ablation – the loss of glacial ice–Melting of glacier–Calving of ice into oceans–Sublimation – the evaporation of iceTo make glaciers•Need cold regions–Topographic highs (mountains), and/or–Landmasses near the poles•Need abundant precipitation–Evaporation rates must be high enough to produce precipitation•Accumulation > Abalation for glaciers to grow•If Ablation > Accumulation, glaciers retreatRelationship of glacier elevation with respect to latitudeGlaciers begin with snow•Snow fall accumulates•Gets compacted and melts•Refreezes to form FIRN (a granular snow)•Firn is compacted, and refrozen to make glacial ice•Snow ~ 80 % air•Glacial Ice ~ 90 % solidsPhotomicrograph of glacial iceGlacial movement•Movement of ice is dependent on snow accumulation and slope–Accumulation is greatest at glacier head–Gravity pulls ice downward & outward–Flows parallel to surface through ablation zone–Flows upward toward the snoutExternal Glacial MovementGlacial movement(ice flow)•Movement is not uniform–Velocity increases from head to snow line•Extending flow–Velocity decreases after snow line•Compressing flow–Local velocity changes with slope–Movement slow or glaciers may SURGEBering Glacier: surged 1 mile in 3 weeks (1993)Internal Glacial movement(ice flow)•Ice is both brittle and ductile–Differential flow velocity creates tensional stress–May occur in any zone–Crevasses form as a result of differential flow•Generally form at ~right angle to flowGlacial movementIce Deforms as it movesGlacier slides on layer of water underneath itBrittle and Ductile BehaviorCrevassesGlacial Erosion•Powerful agents of erosion–Move ALL sizes of sediment–Ice wedging tends to smooth surface•Plucking pulls up loose fragments–Ground-up rock abrades surface•Glacial striations form parallel to the direction of ice flowGlacial Erosion•Dramatically modifies landscapes•Compresses/fractures rocks•Pulverizes material•Glacier “Pluck” material and incorporate it into ice mass•Glaciers rework previous deposits•Carve and smooth rocks and land surfaceGlacial striationsGlacial Deposition•Glacier move vast quantities of sediment•Glacial sediment is called GLACIAL DRIFT•Deposit rocks and sediment in a variety of ways–Directly released as glacier retreats–Sediment from meltwater–Fine grained dust (rock flour) removed from deposits by wind2 Broad categories of Glaciers•Valley (Alpine) Glaciers–Form in the high elevation valleys of mountains–Reshape mountains–PIEDMONT glaciers can form at base of mountains when 2 or more valley glaciers coalesce•Continental (Ice Sheet) Glaciers–Large extent–Result of climate change–Not confined by topographyAlpine (Valley) GlacierAlpine (Valley) GlacierContinental (Ice Sheet) Continental (Ice Sheet) GlacierGlacierValley Glaciers•Create distinctive erosional features–Horns, Cirques, Aretes, Hanging valleys,–U-shaped Valleys•Leave distinctive glacial deposits–Moraines, Braided Streams–Valley lakes may be left behind•Carve coastal valleys that sometimes become “drowned” - FJORDSValley GlaciersValley GlaciersValley GlaciersErosional featuresCirque: a horseshoe- or amphitheater-shaped basin with steep headwalls formed by erosion at the upper end of a glacial troughArete - a narrow, serrated ridge that separates adjacent glacial valleys or adjacent cirquesHorn: a steep-walled, pyramidal peak formed by the headward erosion of cirquesU-shaped valley: a relatively straight valley with very steep walls and a broad, flat floor formed by the movement of a glacier through a stream valleyHanging valley: a tributary glacial valley whose floor is at a higher elevation that that of the main glacial valleyCirqueCirqueHornHornAreteAreteU-shaped valleyHanging valleyHanging valleyFjordFjordLake in U-shaped ValleyErosion and DepositionEndmoraineLateralmoraineContinental Glaciers•Most important glacial system–Modify pre-existing landforms–Cause crustal subsidence (mass of ice)•ISOSTATIC REBOUND – still occurring from last glaciation–Modify drainage systems–Important component of the hydrologic system & climateContinental Glaciers•Ice sheets–Continent-sized ice masses–Antarctic ice sheet is over 4500 m thick–Ice sheets include 95% of all glacier ice•Antarctica & Greenland–Glacial ice accounts for 2.14% of all water on Earth•77.4% of fresh waterBulldozingContinental Glaciers and Ice sheets•Ice caps–Covers large area of mountains or high altitude plains–Ice shows outward radial flow•Ice shelves–Tabular ice bodies resting on the ocean floorContinental GlaciersContinental Glaciers•Glacial Drift – any glacial sediment•Stratified Drift – deposited by running water–Eskers - melt water stream deposits–Kames – Conical